1. Keep your reseach notes organized
2. Keep the notes you take from a source with the source's citation information
3. Use quotation marks around copied and pasted text
4. Keep your own words and a source's words separate
5. Include in-text citations as you write, not after you've finished the paper.
For more on how to integrate sources into a paper, see: Hacker, Diana, and Nancy Sommers. The Bedford Handbook. 8th ed. Boston: Bedford/St. Martins, 2010. Print, pg. 504.
These are some online tools which will help keep your sources organized.
These online sites scan your writing and check against writing on the internet, thus alerting you to inadvertent plagiarism.